The present invention relates to a method for driving a recording head that is composed of a plurality ink-jet heads.
An example of a printer that uses a recording head composed of a plurality of ink-jet heads is an ink-jet color printer, which is equipped with ink-jet heads each for a respective one of four colors of ink (yellow, cyan, magenta, and black) and drives these heads to provide full-color printing. Such a recording head achieves color printing by superimposing each of colored dots of yellow, cyan, magenta, and black on top of the other and therefore has a requirement for strict control of the distance between each head ink nozzle.
However, for printing with high resolution, it is difficult to set precisely the distance between each head ink nozzle to an integral multiple of the pixel pitch. For example, in the case of printing resolutions of 300 to 600 dpi (dots per inch), the distance between printed dots is of the order of 40 to 80 xcexcm. In particular, there arises a considerable degradation in image quality, which is due to periodical unevenness of printing resulting from misalignment of dots due to mechanical displacements at the time of mounting each head. This could be solved by increasing the mechanical precision in mounting each head. To this end, great precision would be required of head mounting members and moreover complex and great precision would also be required for mounting adjustment, making the manufacture difficult and increasing the manufacturing cost.
A method is also known which solves the misalignment of printed dots by displacing the printing timing according to the pitch corresponding to a mounting error between each ink jet head. For example, the misalignment of printed dots in the sub-scanning direction in which a printing medium travels can be corrected by providing a plurality of clocks that permit the printing initiation timing to be selected for each ink jet head and selecting the printing initiation timing according to the displacements of the printing pitch. For example, the provision of a clock four times the normal printing period allows for electrical correction of up to xc2xc pitch of displacement in the sub-scanning direction.
Moreover, a method is known which corrects printing positions by providing a delay circuit for a position displacement for each printing line and displacing the printing timing through the delay circuit. Furthermore, as described in Japanese Unexamined Patent Publication No. 7-156452, a method is also known which utilizes a buffer memory to ensure delay control and high picture quality control.
In summary, the technique that uses a plurality of clocks that allow the printing initiation timing to be selected for each ink jet head requires the clock speed to be increased, which results in complication of control and an increase in cost. The delay circuit-based technique has a problem that control becomes complicated. The techniques disclosed in the patent publication needs a basic clock of N times the highest response frequency for printing and a buffer memory, which complicates control as a result of the increased driving frequency.
It is therefore an object of the present invention to provide a recording head driving method which permits misalignment between printed dot arrangements in both the sub-scanning and main scanning directions through simple control.
According to the present invention, there is provided a method of driving a recording head in which a plurality of ink jet heads each having a large number of ink chambers each provided with an ink nozzle are arranged in parallel with each other in a main scanning direction perpendicular to a direction in which a recording medium moves relative to the heads and are spaced apart from each other by a predetermined distance in a sub-scanning direction in which the recording medium moves, comprising dividing the ink chambers of each of the ink jet heads into N (an integer of two or more) sets each including every N-th ink chamber, placing ink nozzles of N ink chambers each included in a respective one of the N sets in a staggered arrangement, driving the ink chambers on a time division basis for each set, and, when the amount of misalignment between dots recorded by droplets of ink ejected from ink nozzles of a set of ink chambers in a reference head of the heads and dots recorded by droplets of ink ejected from ink nozzles of each set of ink chambers in the other heads than the reference head exceeds one-half of a dot pitch in the sub-scanning direction, changing the order in which the sets of ink chambers are driven on a time division basis to reduce the amount of misalignment of dots below one-half of the dot pitch in the sub-scanning direction.
This method allows alignment error between printed dots in the sub-scanning direction to be corrected through simple control.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.